Configuration

WyW-in-JS can be customized using a JavaScript, JSON or YAML file. This can be in form of:

wyw-in-js.config.js JS file exporting the object (recommended).
wyw-in-js property in a package.json file.
.wyw-in-jsrc file with JSON or YAML syntax.
.wyw-in-jsrc.json, .wyw-in-jsrc.yaml, .wyw-in-jsrc.yml, or .wyw-in-jsrc.js file.

Example wyw-in-js.config.js:

module.exports = {
  evaluate: true,
  displayName: false,
};

Options

evaluate: boolean (default: true):

Enabling this will evaluate dynamic expressions in the CSS. You need to enable this if you want to use imported variables in the CSS or interpolate other components. Enabling this also ensures that your styled components wrapping other styled components will have the correct specificity and override styles properly.
displayName: boolean (default: false):

Enabling this will add a display name to generated class names, e.g. .Title_abcdef instead of `.abcdef'. It is disabled by default to generate smaller CSS files.

variableNameConfig: "var" | "dashes" | "raw" (default: var):

Configures how the variable will be formatted in final CSS.

Possible values

var

Use full css variable structure. This is default behavior.

import { styled } from '@linaria/react';
 
export const MyComponent = styled.div`
  color: ${(props) => props.color};
`;

In CSS you will see full variable declaration

.MyComponent_m1cus5as {
  color: var(--m1cus5as-0);
}

dashes

Removes var() around the variable name. It is useful when you want to control the variable on your own. For example you can set default value for CSS variable.

import { styled } from '@linaria/react';
 
export const Theme = styled.div`
  --font-color: red;
`;
 
export const MyComponent = styled.div`
  // Returning empty string is mandatory
  // Otherwise you will have "undefined" in css variable value
  color: var(${(props) => props.color ?? ''}, var(--font-color));
`;
 
function App() {
  return (
    <Theme>
      <MyComponent>Text with red color</MyComponent>
      <MyComponent color="blue">Text with blue color</MyComponent>
    </Theme>
  );
}

In CSS you will see generated variable name and your default value.

.Theme_t1cus5as {
  --font-color: red;
}
 
.MyComponent_mc195ga {
  color: var(--mc195ga-0, var(--font-color));
}

raw

Use only variable name without dashes and var() wrapper.

import { styled } from '@linaria/react';
 
export const MyComponent = styled.div`
  color: ${(props) => props.color};
`;

In CSS you will see just the variable name. This is not valid value for css property.

.MyComponent_mc195ga {
  color: mc195ga-0;
}

You will have to make it valid:

export const MyComponent = styled.div`
  color: var(--${(props) => props.color});
`;

classNameSlug: string | ((hash: string, title: string, args: ClassNameSlugVars) => string) (default: default):

Using this will provide an interface to customize the output of the CSS class name. Example:
```
classNameSlug: '[title]',
```
Would generate a class name such as .header instead of the default .header_absdjfsdf which includes a hash.

You may also use a function to define the slug. The function will be evaluated at build time and must return a string:
```
classNameSlug: (hash, title) => `${hash}__${7 * 6}__${title}`,
```
Would generate the class name .absdjfsdf__42__header.

Last argument args is an object that contains following properties: title, hash, index, dir, ext, file, name. These properties are useful when you want to generate your own hash:
```
const sha1 = require('sha1');
 
module.exports = {
  classNameSlug: (hash, title, args) => sha1(`${args.name}-${title}`),
};
```
note invalid characters will be replaced with an underscore (_).

Variables
- hash: The hash of the content.
- title: The name of the class.
variableNameSlug: string | ((context: IVariableContext) => string) (default: default):

Using this will provide an interface to customize the output of the CSS variable name. Example:
```
variableNameSlug: '[componentName]-[valueSlug]-[index]',
```
Would generate a variable name such as --Title-absdjfsdf-0 instead of the @react/styled's default --absdjfsdf-0.

You may also use a function to define the slug. The function will be evaluated at build time and must return a string:
```
variableNameSlug: (context) => `${context.valueSlug}__${context.componentName}__${context.precedingCss.match(/([\w-]+)\s*:\s*$/)[1]}`,
```
Would generate the variable name --absdjfsdf__Title__flex-direction.

note invalid characters will be replaced with an underscore (_).

Variables
- componentName - the displayName of the component.
- componentSlug - the component slug.
- index - the index of the css variable in the current component.
- precedingCss - the preceding part of the css for the variable, i.e. flex: 1; flex-direction: .
- preprocessor - the preprocessor used to process the tag (e.g. 'StyledProcessor' or 'AtomicStyledProcessor').
- source - the string source of the css property value.
- unit - the unit.
- valueSlug - the value slug.
overrideContext: (context: Partial<vm.Context>, filename: string) => Partial<vm.Context>

A custom function to override the context used to evaluate modules. This can be used to add custom globals or override the default ones.
```
module.exports = {
  overrideContext: (context, filename) => ({
    ...context,
    HighLevelAPI: () => "I'm a high level API",
  }),
};
```
rules: EvalRule[]

The set of rules that defines how the matched files will be transformed during the evaluation. EvalRule is an object with two fields:
- test is a regular expression or a function (path: string) => boolean;
- action is an Evaluator function, "ignore" or a name of the module that exports Evaluator function as a default export.
If test is omitted, the rule is applicable for all the files.

The last matched rule is used for transformation. If the last matched action for a file is "ignore" the file will be evaluated as is, so that file must not contain any js code that cannot be executed in nodejs environment (it's usually true for any lib in node_modules).

If you need to compile certain modules under /node_modules/ (which can be the case in monorepo projects), it's recommended to do it on a module by module basis for faster transforms, e.g. ignore: /node_modules[\/\\](?!some-module|other-module)/. Example is using Regular Expressions negative lookahead.

The Information about Evaluator, its default setting and custom implementations can be founded it evaluators section of How it works docs

The default setup is:
```
import { shaker } from '@wyw-in-js/transform';
 
[
  {
    action: shaker,
  },
  {
    test: /[\\/]node_modules[\\/]/,
    action: 'ignore',
  },
  {
    test: (filename, code) => {
      if (!/[\\/]node_modules[\\/]/.test(filename)) {
        return false;
      }
 
      return /(?:^|\*\/|;|})\s*(?:export|import)[\s{]/m.test(code);
    },
    action: shaker,
  },
];
```

tagResolver: (source, tag) => string

A custom function to use when resolving template tags.

By default, linaria APIs like css and styled must be imported directly from the package – this is because babel needs to be able to recognize the API's to do static style extraction. tagResolver allows css and styled APIs to be imported from other files too.

tagResolver takes the path for the source module (eg. @linaria/core) and the name of imported tag (eg. css), and returns the full path to the related processor. If tagResolver returns null, the default tag processor will be used.

For example, we can use this to map @linaria/core , @linaria/react or @linaria/atomic where we re-export the module.

{
  tagResolver: (source, tag) => {
    const pathToLocalFile = join(__dirname, './my-local-folder/linaria.js');
    if (source === pathToLocalFile) {
      if (tag === 'css') {
        return require.resolve('@linaria/core/processors/css');
      }
 
      if (tag === 'styled') {
        return require.resolve('@linaria/react/processors/styled');
      }
    }
 
    return null;
  };
}

We can then re-export and use linaria API's from ./my-local-folder:

// my-file.js
import { css, styled } from './my-local-folder/linaria';
 
export const MyComponent = styled.div`
  color: red;
`;
 
export default css`
  border: 1px solid black;
`;

// ./my-local-folder/core.js
export * from '@linaria/core';

babelOptions: Object

If you need to specify custom babel configuration, you can pass them here. These babel options will be used by Linaria when parsing and evaluating modules.
features: Record<string, FeatureFlag>

A map of feature flags to enable/disable. See Feature Flags for more information.

`@wyw-in-js/babel-preset`

The preset pre-processes and evaluates the CSS. The bundler plugins use this preset under the hood. You also might want to use this preset if you import the components outside of the files handled by your bundler, such as on your server or in unit tests.

To use this preset, add @wyw-in-js/babel-preset to your Babel configuration at the end of the presets list:

.babelrc:

{
  "presets": [
    "@babel/preset-env",
    "@babel/preset-react",
+   "@wyw-in-js"
  ]
}

The babel preset can accept the same options supported by the configuration file, however it's recommended to use the configuration file directly.

Changelog Feature Flags